Several methods for detection of small quantities of particles are known in the art, for example, nephelometric and turbidimetric methods as well as methods referred to as dynamic-light-scattering (DLS).
In nephelometric and turbidimetric methods, the Tyndall effect is used in which the illumination of a small particle produces wide-angle scattered light. The scattering of the light can be determined, either by measuring the decrease of intensity of the incident light beam after passing through the scattering medium or by determining the intensity of the laterally deflected light. The former case is referred to as the method of turbidimetry or measurement of extinction, and the latter case as nephelometry proper, or tyndallometry.
Methods referred to as dynamic-light-scattering (DLS) methods afford another approach. In these methods, just one (or a few) points on the light sphere surrounding the particle are observed but in addition, the brightness modulation caused by the Brownian movement is analysed. By focusing on a tiny monitoring volume, one attempts to reduce the interference due to the superposition of scattered light from several particles. Consequently, a particle passes very quickly through a tiny illuminated volume, so that the analysing optoelectronics must detect significant fluctuation frequencies. A large amount of information is supplied by the complex signal processing, so that these systems are only conditionally useful for quantitative analysis.
The detection methods of the prior art exhibit further disadvantages. It should first be mentioned that, although the detection sensitivity of the methods just described has strongly increased in recent years, there still is a strong need in the most diverse fields for detection methods having higher sensitivity. Furthermore, the detection methods of the prior art still require comparatively large amounts of samples, which particularly in methods of medical technology may put stress on the person being examined.
It is an object of the present invention, therefore, to provide a method for the detection of small quantities of particles which exhibits a higher sensitivity than the methods of the prior art. Furthermore, such a method should require less dilution of the sample and/or a lower minimum amount of sample, should be suitable for sample analyses on a larger scale, and after elementary training should also be realisable by personnel without special prior experience. Furthermore, it is an object of the invention to provide a device for the detection of small quantities of particles.
This object is attained by providing a method for the detection of small quantities of particles by the detection of antigen-antibody precipitates, the method comprising: providing a sample fluid that essentially contains particles with a given maximum particle size, the particles having at least two antibody binding sites; providing a fluid containing antibodies that contains essentially particles with a given maximum particle size; contacting the sample fluid with the fluid containing antibodies, which yields a reaction fluid where in the presence of a particle having at least two antibody binding sites, the antibody can form an antigen-antibody precipitate; directing a light beam through the reaction fluid; detecting a signal by measuring with a photodetector the extinction at the light-dark boundary of the cone of light produced when the light generated by the laser is passing through the measuring cell containing the reaction fluid, the strength of the signal depending on the size and number of the antigen-antibody precipitates formed.
The present invention further provides a device for the detection of small quantities of particles which comprises: a light source, a measuring cell, and a photodetector that is designed for measuring the extinction at the light-dark boundary of the cone of light produced when the light generated by the laser is passing through the measuring cell containing the particles in a fluid. The light scattered forward forms a cone, and the photodetector is aimed at the light-dark boundary thereof. Laser and photodetector are essentially axially aligned, though offset in such a way that the laser beam very narrowly passes by the photodetector.